What is setBounds and how do I use it?

问题

I cannot find anything on setBounds, what it is for, or what its function actually is. Could someone clear me up on this? Thanks so much!

回答1:

You can use setBounds(x, y, width, height) to specify the position and size of a GUI component if you set the layout to null. Then (x, y) is the coordinate of the upper-left corner of that component.

回答2:

setBounds is used to define the bounding rectangle of a component. This includes it's position and size.

The is used in a number of places within the framework.

It is used by the layout manager's to define the position and size of a component within it's parent container.
It is used by the paint sub system to define clipping bounds when painting the component.

For the most part, you should never call it. Instead, you should use appropriate layout managers and let them determine the best way to provide information to this method.

回答3:

This is a method of the java.awt.Component class. It is used to set the position and size of a component:

setBounds
public void setBounds(int x,
                  int y,
                  int width,
                  int height) 
Moves and resizes this component. The new location of the top-left corner is specified by x and y, and the new size is specified by width and height. Parameters:

x - the new x-coordinate of this component

y - the new y-coordinate of this component

width - the new width of this component

height - the new height of this component

x and y as above correspond to the upper left corner in most (all?) cases.

It is a shortcut for setLocation and setSize.

This generally only works if the layout/layout manager are non-existent, i.e. null.

回答4:

There is an answer by @hexafraction , He had specified the x and y to be top right corner which is wrong, those are top left corner .

I have also provided the source please check it.

public void setBounds(int x,
             int y,
             int width,
             int height)

Moves and resizes this component. The new location of the top-left corner is specified by x and y, and the new size is specified by width and height. This method changes layout-related information, and therefore, invalidates the component hierarchy.

Parameters:

x - the new x-coordinate of this component

y - the new y-coordinate of this component

width - the new width of this component

height - the new height of this component

source:- setBounds

回答5:

Actually, a Swing component does have multiple dimensions, as:

current size - setSize() and setBounds() sets this
minimum size - setMinimumSize() sets this
preferred size - setPerferredSize() sets this
maximum size - setMaximumSize() sets this.

SetBounds is a shortcut for setting current size plus location of the widget if you don't use any layout manager.

If you use a layout manager, it is the responsibility of the layout manager to lay out your components, taking into account the preferred size you set, and ensuring that the comonent never gets smaller than its minimumSize or bigger than its maximumSize.

In this case, the layoutManager will call setSize (or setBounds), and you can not really control the position or dimension of the component.

The whole point of using a layout manager is to have a platform and window-size independent way of laying out your components automatically, therefore you don't expect to call setSize from your code.

(Personal comment: There are buggy layout managers, I personally hate all of them and rolled my own, which offers the flexibility of MigLayout without the learning curve.)

回答6:

The way that Java Swing UIs work is that for each JPanel there is always a LayoutManager that decides on where to exactly place your components. Each layout managers works differently, so if you use for example a BorderLayout, setBounds() is not used by the LayoutManager, instead component placement is decided by East,West,South,North,Center.

For the NullLayoutManager (in case you used new JPanel(null)) however, each component has to have an x and y coordinate. Stupid Sidenote: if your UI would be three-dimensional there would also be a z coordinate.

So with public void Component.setBounds(int x, int y, int width, int height) you specify where your component is placed and how many pixel it is wide and high.

Here's an example:

import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class JTableInNullLayout
{
  public static void main(String[] argv) throws Exception {

      JPanel panel = new JPanel(null);

      JLabel helloLabel = new JLabel("Hello world!");
      helloLabel.setBounds( 10, 50, 60, 20 ); // x, y, width, height
      panel.add(helloLabel);

      JFrame frame = new JFrame();
      frame.add(panel);
      frame.setPreferredSize( new Dimension(200,200));
      frame.pack();
      frame.setVisible(true);
  }
}

回答7:

here's a short paragraph from this article How to Make Frames (Main Windows) - The Java Tutorials - Oracle that explains what setBounds method does in addition to some other similar methods:

The pack method sizes the frame so that all its contents are at or above their preferred sizes. An alternative to pack is to establish a frame size explicitly by calling setSize or setBounds (which also sets the frame location). In general, using pack is preferable to calling setSize, since pack leaves the frame layout manager in charge of the frame size, and layout managers are good at adjusting to platform dependencies and other factors that affect component size.

the parameters of setBounds are (int x, int y, int width, int height) x and y are define the position/location and width and height define the size/dimension of the frame.

来源：https://stackoverflow.com/questions/19415170/what-is-setbounds-and-how-do-i-use-it

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java

setbounds